The leading cause of lower back pain arises from rupture or degeneration of lumbar intervertebral discs. Pain in the lower extremities is caused by the compression of spinal nerve roots by a bulging disc, while lower back pain is caused by collapse of the disc and by the adverse effects of articulation weight through a damaged, unstable vertebral joint.
In some cases, when a patient having a collapsed disc moves in extension (e.g., leans backward), the posterior portion of the annulus fibrosus may further compress and extend into the spinal canal. This condition (called “spinal stenosis”) produces a narrowing of the spinal canal and impingement of tissue upon the spinal cord, thereby producing pain.
There have been numerous attempts to provide relief for these afflictions by providing a spacer that inserts between adjacent spinous processes present in the posterior portion of the spinal column. In general, these interspinous implants are adapted to allow flexion, rotation, translation and lateral bending movement in the patient, but resist or limit extension.
U.S. Pat. No. 6,068,630 (“Zuchermann”) discloses a spinal distraction implant that alleviates pain associated with spinal stenosis by expanding the volume in the spinal canal or neural foramen. Zucherman discloses a plurality of implants having a body portion and lateral wings. The body portion is adapted to seat between the adjacent spinous processes, while the wings are adapted to prevent lateral movement of the body portion, thereby holding it in place between the adjacent spinous processes. The designs disclosed in FIGS. 15, 80 and 84 of Zuchermann comprise central body having an integral wing.
Although the Zucherman device achieves spinal distraction, it nonetheless possesses some limitations. First, it is a multi-piece design, and so is subject to wear and implantation complexity. Second, since the Zuchermann central bodies have at least one integral wing, the clinician may encounter difficulty in sizing the central body independently of delivering the lateral wings. Third, the expansive geometry of the disclosed devices may not lend itself to minimally invasive surgical techniques seeking to conserve muscle mass and soft tissue in the regions adjacent the spinous processes.